[BOLT] Fix hot_end symbol update with user function order

Summary:
If no profile data is provided, but only a user-provided order
file for functions, fix the placement of the __hot_end symbol.

(cherry picked from FBD22713265)

bolt/src/Passes/BinaryPasses.cpp

@@ -13,6 +13,7 @@
 #include "BinaryPasses.h"
 #include "ParallelUtilities.h"
 #include "Passes/ReorderAlgorithm.h"
+#include "Passes/ReorderFunctions.h"
 #include "llvm/Support/Options.h"
 
 #include <numeric>
@@ -60,6 +61,7 @@ extern cl::opt<bolt::MacroFusionType> AlignMacroOpFusion;
 extern cl::opt<unsigned> Verbosity;
 extern cl::opt<bool> EnableBAT;
 extern cl::opt<bool> UpdateDebugSections;
+extern cl::opt<bolt::ReorderFunctions::ReorderType> ReorderFunctions;
 extern bool isHotTextMover(const bolt::BinaryFunction &Function);
 
 enum DynoStatsSortOrder : char {
@@ -1138,7 +1140,9 @@ void AssignSections::runOnFunctions(BinaryContext &BC) {
   if (!BC.HasRelocations)
     return;
 
-  const auto UseColdSection = BC.NumProfiledFuncs > 0;
+  const auto UseColdSection =
+      BC.NumProfiledFuncs > 0 ||
+      opts::ReorderFunctions == ReorderFunctions::RT_USER;
   for (auto &BFI : BC.getBinaryFunctions()) {
     auto &Function = BFI.second;
     if (opts::isHotTextMover(Function)) {

bolt/test/X86/Inputs/user_func_order.txt

@@ -0,0 +1,2 @@
+main
+fib

bolt/test/X86/user-func-reorder.c

@@ -0,0 +1,43 @@
+/* Checks that BOLT correctly processes a user-provided function list file,
+ * reorder functions according to this list, update hot_start and hot_end
+ * symbols and insert a function to perform hot text mapping during program
+ * startup.
+ */
+#include <stdio.h>
+
+int foo(int x) {
+  return x + 1;
+}
+
+int fib(int x) {
+  if (x < 2)
+    return x;
+  return fib(x - 1) + fib(x - 2);
+}
+
+int bar(int x) {
+  return x - 1;
+}
+
+int main(int argc, char **argv) {
+  printf("fib(%d) = %d\n", argc, fib(argc));
+  return 0;
+}
+
+/*
+REQUIRES: system-linux
+
+RUN: %host_cc %s -o %t.exe -Wl,-q
+
+RUN: llvm-bolt %t.exe -relocs=1 -lite -reorder-functions=user  \
+RUN:   -function-order=%p/Inputs/user_func_order.txt -o %t
+RUN: nm -ns %t | FileCheck %s -check-prefix=CHECK-NM
+RUN: %t 1 2 3 | FileCheck %s -check-prefix=CHECK-OUTPUT
+
+CHECK-NM:      W  __hot_start
+CHECK-NM:      T main
+CHECK-NM-NEXT: T fib
+CHECK-NM-NEXT: W __hot_end
+
+CHECK-OUTPUT: fib(4) = 3
+*/